Process of esterifying alkaline earth aconitates



United States Patent Office 2,813,117 Patented Nov. 12, 1957 PRfifiESS F ESTERHFYTNG ALKALINE EARTH ACONITATES Earl J. Roberts, New Orleans, La., assignor to the United States of America as represented by the Secretary of Agriculture No Drawing. Application January 3, 1955, Serial No. 479,684

3 Claims. (Cl. 260-485) (Granted under Title 35, U. S. Code (1952), see. 266) A non-exclusive, irrevocable, royalty-free license in the invention herein described, for all governmental purposes, throughout the world, with the power to grant sublicenses for such purposes is hereby granted to the Government of the United States of America.

This invention relates to the production of aconitic esters from alkaline earth aconitates. More particularly, the invention provides an improved single step neutralization-esterification process which is adapted for continuous operation.

Aconitic acid occurs in sugarcane and sugar beets and alkaline earth aconitates are available as by-products of the manufacture of sugar. In general, such alkaline earth aconitates are relatively impure salts from which it is not feasible to isolate the aconitic acid for separate esterification.

An object of the present invention is to provide a process of producing esters from alkaline earth aconitates in which process the aconitic acid is both substantially completely liberated from the alkaline earth aconitates and esterified, in a single step neutralization-esterification. A further object is to provide such a process in which water soluble alcohols can be substantially completely esterified as readily as water immiscible alcohols.

In general, in accordance with the present invention, aconitic esters are produced by: mixing an alkaline earth aconitate with its neutral ester equivalent (based on 100% purity) plus at least about a 90% by weight excess of at least one normally liquid monohydric alcohol boiling below about 200 C. in which a hydroxyl group is the only group reactive toward acids, alkenols having from 3 to 5 carbon atoms being particularly preferred, at least about 150% of the weight of the alkaline earth aconitate of an inert, liquid, water immiscible organic solvent boil ing below about 115 C., and the neutral equivalent of the alkaline earth aconitate (based on 100% purity) plus an excess of about 2 to by weight of a strong acid esterification catalyst; reacting the mixture by maintaining it at a temperature at which Water is formed, preferably at atmospheric pressure, and fractionally distilling off the water as it is formed for substantially as long as the formation of water occurs; mechanically removing alkaline earth salts of the strong acid from the reaction products; and recovering an aconitic ester from the remaining reaction products. In a preferred embodiment of the invention, after the strong acid-alkaline earth salts have been removed from the reaction products, the solvent and unreacted alcohol are isolated by fractional distillation, and recycled as part of the solvent and alcohol to be reacted with an additional quantity of alkaline earth aconitate.

The alkaline earth aconitate can be substantially any crude or purified salt containing at least about 40-60% of aconitate ions.

The normally liquid monohydric alcohol boiling below about 200 C. in which a hydroxyl group is the only group reactive toward acids can be a primary, secondary,

or teritary alcohol containing groups such as ether groups, halogen atoms, ketone groups and the like, which are substantially unreactive toward either strong or weak acids. In general, however, the use of primary or secondary hydrocarbon alcohols is preferred; and the use of primary alkenols or alkanols having from 3 to 5 carbon atoms is particularly preferred. Illustrative examples of suitable alcohols include n-propyl, n-butyl, n-hexyl, 2-ethylhexyl, isopropyl, tertiary butyl, 1,3-dimethyl butyl, cyclohexyl, allyl, l-propenyl, methallyl, 4-pentenyl, 2- ethoxyethyl, 2,3-dibromopropyl, 2-nitrobutyl, acetylmethyl, and the like alcohols. The primary propyl, butyl, or amyl alcohols and their terminally ethylenic analogs such as allyl, methallyl, or 4-pentenyl alcohols are particularly preferred.

The liquid solvents can be substantially any water immiscible organic liquid boiling below about 115 C. which is inert toward alcohols and acids and which is a solvent for aconitic esters. Illustrative examples of suitable solvents include hydrocarbons such as the pentanes, benzene, toluene, and the like; others such as diethyl ether, dibutyl ether, diphenyl ether and the like; water insoluble ketones such as methyl, butyl ketone, diisopropyl ketone, and the like. The use of an aromatic hydrocarbon solvent is preferred.

The strong acid esterification catalyst can be concentrated sulfuric, hydrochloric, or phosphoric acid; or a benzene, toluene or the like sulfonic acid. The use of a non-volatile acid such as concentrated sulfuric or phosphoric acid is preferred. Sulfuric acid is particularly suitable.

The alkaline earth aconitate, the alcohol, the solvent, and the strong acid can be mixed in any order. However, in general, it is preferred to first dissolve the alcohol in the solvent, then suspend the alkaline earth aconitate in the solution, and then add the strong acid.

The proportions of the components of the neutralization-esterification reaction mixture can be varied widely. The use of at least by weight of excess alcohol tends to force the esterification reaction (which is an equilibrium reaction) to rapidly use up substantially all of the aconitic acid. The use of materially smaller amounts tends to lower the rate of reaction. Where the alcohol has a limited water solubility, materially larger excesses of the alcohol can be used; but, in general; the use of an excess of from 50 to is preferred. The use of an amount of solvent which is at least about of the weight of the alkaline earth aconitate provides a non-viscous mixture of both the reactants and the reaction products from which the strong acid alkaline earth salts can readily be mechanically removed by the usual procedures such as filtration, centrifugation and the like. Particularly where the alcohol is somewhat water soluble the use of a materially smaller amount of solvent tends to cause difficulties in the mechanical removal of the salts. Where the alcohol is relatively insoluble in water, a somewhat smaller excess of solvent can be used in conjunction with the use of a relatively large excess of the alcohol; since a part of the excess alcohol tends to act as the solvent. The use of very large amounts of solvent tends to lower the rate of reaction. In general, the use of from about 100 to 300% of the weight of the aconitic acid of the solvent is preferred. The amount of strong acid esterification catalyst in excess of that required to decompose all of the alkaline earth salts of from about 1 to 10% by weight provides a desirably rapid esterific tion reaction without undue loss of the strong acid. The optimum amounts to be used depend primarily upon the acid involved. In the case of concentrated sulfuric acid, the use of an excess of from about 2 to 5%, is preferred.

The esterification reaction can be conducted under pressures above or below normal atmospheric pressure; but,

3 in general,- the use of atmospheric pressure is preferred. 7 When the reaction is conducted under atmospheric pressure, the water can readily be fractionally distilled away from the reaction mixture using the relatively low cost apparatus designed for the employment of atmospheric pressure.-

The reaction temperature is preferably the boiling point of the reaction mixture under normal atmospheric pressure. However, where a more rapid reaction is desired, a higher pressure can be employed to raise the boiling point of the mixture. Where it is desired to obtain a relatively rapid rate of reaction without the use of a higher temperature a reduced pressure can be employed to" cause the water to" distill below the temperature it would distill under atmospheric pressure. In most cases the water distills in the form of a low boiling azeotr'ope of water, the solvent, and/ or the alcohol.

In the course of the present process, relatively pure mixed calcium and manganese salts of the strong acid used are formed in relatively large amounts. Whenever there is a demand for such salts of any particular strong acid e'st'erification catalyst, the selection of such an acid enables the production of its salts as a by-product of the process of producing the aconitic esters.

In general, the aconitic esters can be recovered from the portion of' the reaction products remaining after the removal of the alkaline earth strong acid salts by the usual processes of recovering esters from hydrocarbon solutions, such as fractional distillation or selective extraction, and purified by the usual processes of purifying organic esters. The removal and purification of the esters by means of vacuum fractional distillation is preferred.

The process of the present invention can advantageously be conducted as a continuous process by using continuous mechanical means for removing the alkaline earth salts of the strong acid used and for the fractional distillation of the reaction products. In this connection, the unreacted alcohol and the solvent are isolated from the reaction products, preferably by a fractional distillation, and are separately collected, or collected as a mixture of solvent and alcohol, and re-used as a portion of the alcohol and solvent which are mixed with alkaline earth aconitates.

The following examples are illustrative of certain de-' tails of the invention.

Example 1 554 grams (1 mole) of calcium-magnesium aconitate was suspended in 680 grams (12 moles (theory+100%)) of allyl alcohol and 1000 cc. (about 200%) of toluene in a three-necked flask fitted with a stirrer, dropping funnel and refiux condenser with return through a water trap. The stirrer was started and as soon as refluxing began 320 grams (theory+ g.) of concentrated sulfuric acid was added dropwise from the dropping funnel. Heating was continued with constant stirring until no more water separated. The inorganic salts were then filtered off and washed free of ester with commercial hexane. The combined filtrate and washings were washed free of acid with 5% sodium hydroxide and then washed with water until neutral. The solvents and excess alcohol were removed by heating on the steam bath under about 15 mm. pressure and the ester was distilled. Yield 400 4 grams (67% of theoretical) boiling at 127 c. at microns pressure and 100 drops per minute.

Example 2 554 grams (1 mole) of calcium-magnesium aconitate was suspended in 888 grams (12 moles (theory-l-100%)) of secondary butyl alcohol and 1000 cc. of toluene. The esterification was carried out as described for triallyl aconitate. Yield 514 grams of theoretical) boiling at 150 C. at 10 microns and 100 drops per minute.

1 claim:

1. A process for the production of aconitic esters, comprising: mixing an alkaline earth aconitate with its neutral ester equivalent (base on 100% purity) plus at least about a by weight excess of at least one normally liquid mon'ohydric alkenolhaving from 3 to 5 carbon atoms, boiling below about 200 C., and in which a hydroxyl group is the only group reactive toward acids, at least about 150% of the weight of the alkaline earth aconitate of an inert: liquid water immiscible organic solvent boiling below about 115 C., and the neutral equivalent of the alkaline earth aconitate (based on purify) plus an exces of about 2 to 10% by weight of a strong acid esterification catalyst; reacting the mixture by maintaining it at a temperature at which water is formed at atmospheric; pressure and fractionally distilling off the water as it is formed for substantially as long as water is formed; mechanically removing alkaline earth salts of the strong acid from the reaction products; and recovering an aconitie ester from the remaining reaction products.

2.- A process for the production of triallyl aconitate, comprising: mixing an alkaline earth aconitate with its neutral ester equivalent (based on 100% purity) plus at least about 90% by weight excess of allyl alcohol, at least about 150% by weight of the alkaline earth aconifate of an inertliquid water immiscible organic solvent boiling below about C., and the neutral equivalent of the alkaline earth aconitate (base on 100% purity) plus an excess of from Zito 10% by weight of concentrated sulfuric acid; reacting the mixture by maintaining it at a temperature at which water is formed at atmospheric pressure and fractionally distilling off the water as it is formed for substantially as long as the formation of water occurs; mechanically removing alkaline earth Reference's' Cited in the file of this patent UNITED STATES PATENTS 1,448,506 1 111115161 of al. 1 Sept. 7, 1948 2,475,629 Meincke July 12, 1949 2,645,658 Reeves July 14,- 1953 2,708,676 Baggett et al. May 17, 1955 2,742,495 Nawiasky et al Apr. 17, I956 

1. A PROCESS FOR THE PRODUCTION OF ACONITIC ESTERS, COMPRISING: MIXING AN ALKALINE EARTH ACONITATE WITH ITS NEUTRAL ESTER EQUIVALENT (BASE ON 100% PURITY) PLUS AT LEAST ABOUT A 90% BY WEIGHT EXCESS OF AT LEAST ONE NOR-MALLY LIQUID MONOHYDRIC ALKENOL HAVING FROM 3 TO 5 CARBON ATOMS, BOILING BELOW ABOUT 200*C., AND IN WHICH A HYDROXYL GROUP IS THE ONLY GROUP REACTIVE TOWARD ACIDS, AT LEAST ABOUT 150% OF THE WEIGHT OF THE ALKALINE EARTH ACONITATE OF AN INERT LIQUID WATER IMMISCIBLE ORGANIC SOLVENT BOILING BELOW ABOUT 115*C., AND THE NEUTRAL EQUIVALENT OF THE ALKALINE EARTH ACONITATE (BASED ON 100% PURITY) PLUS AN EXCES OF ABOUT 2 TO 10% BY WEIGHT OF A STRONG ACID ESTERIFICATION CATALYST; REACTING THE MIXTURE BY MAINTAINING IT AT A TEMPERATURE AT WHICH WATER IS FORMED AT ATMOSPHERIC PRESSURE AND FRACTIONALLY DISTILLING OFF THE WATER AS IT IS FORMED FOR SUBSTANTIALLY AS LONG AS WATER IS FORMED; MECHANICALLY REMOVING ALKALINE EARTH SALTS OF THE STRONG ACID FROM THE REACTION PRODUCTS; AND RECOVERING AN ACONITIC ESTER FROM THE REMAINING REACTION PRODUCTS. 